[Vorbis] OGG decoding/multi-channel mixing

[Joshua Root]

Joost Meijles wrote:
> Hi All,
> 
> Currently I am investigating how interesting OGG is for me.
> The most important requirements are:
> - Decoding on embedded hardware, ARM7 or ARM9.
> - Mixing multiple audio streams/files on embedded hardware
> 
> First of all how difficult is it to decode OGG on an ARM7/9 processor? I read that OGG decoding needs floating point support?

Just to be clear, Ogg is a container format (and is not written in
all-caps since the name is not an acronym), with Vorbis being the most
common audio codec used with Ogg.

There is a fixed-point version of the Vorbis decoder, called Tremor.
Check it out on <http://www.xiph.org/>. There's also a mailing list
devoted to it. I'm not sure how much CPU it needs in absolute terms.

> Finally is it possible to mix OGG streams without first decoding them to PCM? I found a program that is mixing multiple OGG streams called "mixplayd", but I wasn't able to figure out if this program is first decoding and than mixing or if it is mixing native OGG and than decoding one mixed OGG stream. 

Is there any commonly used lossy audio codec for which this is possible?
It doesn't seem like the transformations used would lend themselves to
the task, but I could easily be wrong.

Cheers,
Josh